Erosion resistant flow conduit

ABSTRACT

A particulate-accommodating fluid flow directing apparatus comprises a failure detection housing containing a flow directing insert, the housing serving as a pressure boundary; failure at any location along the insert being detectable by means associated with the housing. The insert can be manufactured of erosion resistant materials, including non-ductile materials such as ceramics. The insert is sealed to the housing at an inlet and a discharge forming a pressure chamber between the insert and housing. The pressure chamber can be maintained at a pad pressure complementary to the process pressure, the pad pressure being maintained and monitored for indication of insert failure.

FIELD

The disclosed embodiment relates to apparatus for fluid flow conduitsfor accommodating erosion prevalent in changes of direction ofparticulate-laden flow streams, and more particularly to an erosionresistant pipe bend insert supported within a pressure housing providingstructure support of the insert and failure detection.

BACKGROUND

Gas and oil wells often produce fluids containing particulates whichcause premature failures in piping. A wellhead conducts a fluid flowstream through equipment including chokes and metering apparatus.Particulates such as sand can be produced from the gas or oil formationitself or, in many cases, or introduced sand such as fracturing sandbeing recovered after stimulation operations. If desanding apparatus isnot used, or not used long enough, upon initiating production, the sandconcentration though downstream production piping causes accelerateddegradation. The placement and orientation of various equipment canresult in the occasional bend, including right angle or 90 degreeelbows. The elbows result in a change in direction and marked increasein the erosive effect of contained particulates. When flow direction ischanged in the bend, the particulates do not parallel the fluid flow,but resist a trajectory change and move against the outside of the turn,eroding the contact points. The erosions patterns in bends, tees, andblind tee connections can be complex, the ultimate point of failure fromerosion being somewhat un-predictable.

Internal erosion of the piping is not readily detected until failure andfailure can be catastrophic, the fluid flow such as gas being underpressure, flammable and often containing H₂S which is fatal in even lowconcentrations. This establishes the need for a effective device.

One prior art early warning device is that disclosed in U.S. Pat. No.7,246,825, which provides an elbow in a block having a main fluidpassageway. The block further contains a matrix of passageways,separated from the main passageway by sufficient wall material thatexpected erosion to destruction will occur only over a reasonableoperations period. The matrix of passageways is maintained at a low anddifferential pressure to that of the main flow stream. Erosioneventually breaks through the wall material, connecting the flow withthe matrix of passageways. The matrix pressure is monitored and when thedifferential pressure climbs to the pressure in the process stream,breakthrough is detected and an orderly turnaround can be scheduled forreplacement of the block. The matrix is rated for the process pressure.One shortcoming is that the matrix of holes have to intersect the areathat was being eroded, being an uncertain science. The matrix cannotprovide 100% coverage as the holes are inside the pressure boundary.

Another form of prior art apparatus includes ceramic lined pipes andmachined ceramic elbows.

The ceramic material of the elbow forms part of the pressure boundaryand is therefore required to have sufficient tensile strength to meetthe pressure requirements. This requires special ceramics or overlythick material. As well, some regulatory codes would require specialexemptions to use this material.

SUMMARY

Generally, a particulate-accommodating fluid conduit and failuredetection apparatus is disclosed herein. In an embodiment, the conduitis a flow directing insert and failure detection is provided by locatingthe insert wholly within a failure detection housing serving as apressure boundary; failure at any location therealong being detectableby means associated with the housing. The conduit or flow directinginsert can be manufactured of erosion resistant materials, includingnon-ductile and ceramics not normally permitted by regulatory codes forpressure applications. The flow directing insert is wholly supported andcontained within a pressure chamber of the failure detection housing.The pressure chamber and housing form a surrounding pressure boundarymanufactured from conventional materials and authorized underappropriate regulatory codes for apparatus and operations underpressure. Within the pressure chamber, an intermediate fluid pad isformed about a substantial length of the flow directing insert, betweenthe insert and the housing. The insert is sealed to the housing at aninlet and a discharge to separate the fluid flow from the fluid pad.

The fluid flow directing insert can be used in wellhead piping,typically conveying particulates and which is particularly susceptibleto erosion.

In an embodiment, failure of an insert can be detected by monitoringchanges in the pressure between the fluid stream and the fluid pad.Accordingly, should the flow directing insert fail at any locationtherealong, the fluid pad is exposed to the fluid flow and pressuresequilibrate, signalling failure and need for replacement.

In other embodiments, similar inserts and housings can be provided forother challenging erosive flow arrangements including blinded tee's,reducers, and headers. Accordingly, the term flow directing insertincludes a range of piping from straight runs through 90 degree elbows,a reducer also being contemplated and included herein, the fluid flowwithin the reducer being guided from one flow regime to another andresulting in enhanced risk of erosion.

In one aspect, flow directing apparatus is provided for conveying afluid flow comprising a housing forming a pressure boundary, and a flowdirecting insert within the housing. The flow directing insert is fitsealably within the housing for forming a pressure chamber about theinsert and between the insert and the housing, the insert having aninlet end for receiving the fluid flow and a discharge end fordischarging the fluid flow. The insert can cause a trajectory change inthe fluid flow such as a bend in the piping. The insert can bereplaceable.

In another aspect, the fluid flow contains particulates and the insertis a wear resistant material, such as a non-ductile material likeceramic, resistive to erosion from the particulates.

In another aspect directed to insert failure detection, the flowdirecting apparatus further comprises a pressure monitor connected tothe pressure chamber for detecting a pressure change in the pad pressurebeing indicative of failure of the insert. The process and pad pressurecan be maintained at a pressure differential, the pressure differentialbeing maintained by a make-up pressure source and may also include aregulator for introducing make-up pressure as necessary to maintain thedifferential pressure between the fluid flow and the pressure chamber.

In another aspect, the disclosed flow directing apparatus can beemployed in wellhead piping as a flow bend, such as a 90 degree elbow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of one embodiment of a flow directinginsert and pressure boundary housing fit into wellhead piping and havingflanged connections to wellhead piping, the fasteners in this figure andothers being omitted for simplicity of view;

FIG. 1B is an enlarged view of an inside bend of an insert fit with ableed port for equilibrating supportive pressures between the fluid flowand the fluid pad;

FIG. 2A is a view of one embodiment of the flow directing insert fit toa pressure boundary housing and having a pressure sensing system;

FIG. 2B is a view of one embodiment of the flow directing insert fit toa pressure boundary housing and having a pressure sensing anddifferential pressure maintenance system;

FIG. 3A is a cross-sectional view of a liquid accumulator located in thepressure housing for pressure maintenance against a fluid pad for aliquid-filled pressure chamber for the pressure boundary housing;

FIG. 3B is a cross-sectional view of an optional liquid accumulator as adevice separate from the pressure housing;

FIG. 4 is a cross-sectional view of a pressure-differential reductionpiston loop for automatic pressure maintenance of the fluid pad for aliquid-filled pressure chamber;

FIG. 5 is an exploded view of one methodology for installation of aninsert for replacement or upon initial installation;

FIG. 5A through 5C are various views of an embodiment of an insertretainer ring, FIG. 5A illustrating a plan view of a retainer ring oftwo half-circular and overlapping rings, FIG. 5B illustrating a sideview of assembled rings of FIG. 5A, and FIG. 5C illustrating yet anotherembodiment of a four-segmented retainer ring; and

FIG. 6 is a partial cross-section view of the connection of one end ofthe insert to the pressure boundary housing.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1A, an erosion resistant conduit 10 and a pressureboundary housing 20 is disclosed herein. The housing 20 supports theconduit 10 and enables detection of failure thereof. The conduit directsthe flow of fluid and is exposed to the action of erosion, such as byerosive particulates contained in a process stream or fluid flow Fconducted therethrough. Conduits including bends are particularlysubject to accelerated erosion including aggravating factors such as theparticulates impacting the bend wall, undergoing a change in momentumand the boundary layer is breached.

An extensive analysis of erosive wear in piping systems can be found in“Recommended Practice RP 0501 Erosive Wear In Piping Systems”, Rev.4.2-2007 by Det Norske Veritas.

Herein, at least a flow directing or bend portion 12 of the conduit 10is manufactured as a flow directing insert 14 formed of erosionresistant materials, including those not normally permitted byregulations for pressure applications. Such materials includenon-ductile or brittle materials.

As shown in FIGS. 1A, 2A through 5, the arrangement of the housing 20accommodates the form of insert 14. The example flow directing insert 14has a 90 degree bend and the housing 20 is provided with inlet andoutlet ports at 90 degrees. A housing for a reducer insert would havealigned inlet and outlet ports, the housing for a 45 degree elbow havinginlet and outlets oriented at 45 degrees and so on.

Such materials are firstly and generally unacceptable under regulatorycodes for the instances as forming a pressure boundary to theenvironment, and secondly and related thereto, a failure of suchmaterials can be catastrophic, the insert 14 is wholly supported andcontained within a pressure chamber 22 of the failure detection housing20 forming a surrounding pressure boundary that can be manufactured fromconventional materials authorized under appropriate codes for pressureoperations. In one aspect, pressure P1 of fluid flow F in the insert andpressure P2 of the pressure boundary can be controlled to an acceptablepressure differential dp (|P1−P2|) for controlling the magnitude ofpressure-induced stresses in the insert 14. Further, in another aspect,fluid release due to failure of the insert 14 is constrained by thehousing 20. As the housing 20 need not be designed for sustained fluidflow conditions, detection of a failure of the insert 14 can providedfor an orderly shutdown and replacement thereof.

Responsive to both above-identified aspects, within the pressure chamber22, an intermediate fluid pad B can be formed about a substantial lengthof the flow directing insert, between the insert 14 and the housing 20.The fluid pad B is maintained at a threshold pressure P2 selected to berelated to, and in one embodiment, different that the fluid flowpressure P1. The insert 14 is sealed to the housing 20 at an insertinlet end 24 and an insert discharge end 26 to separate the fluid flow Ffrom the fluid pad B. Accordingly, should the flow directing insert 14fail at any location therealong, the fluid pad B is exposed to the fluidflow F and pressures therebetween equilibrate, signalling failure andneed for replacement of the insert 14.

Pressure sensors and pressure differentials can be monitored forsignalling failure and, in one embodiment, for initiating closure of anemergency shutdown (ESD) valve located in the piping upstream of theinsert 14, such as that in wellhead piping between the wellhead and thehousing 20. In other embodiments, an alarm can alert an operator of theneed for remedial action.

In an embodiment, one suitable material for the flow directing insert 14is a highly erosion resistant material such as that selected from theceramics. Such materials are typically brittle and unsuitable for use asthe pressure boundary in pressure applications according to applicablecodes. One material that is usable includes silicon nitrile which isconventionally cost prohibitive when forming the entirely of acommercial structure. Other lower cost ceramics are quite brittle andare not listed in the various codes for pressure containment includingNACE, ASME, CSA. As a consequence, use of such materials usuallyrequires special applications and permission before use in a pressurizedenvironment.

Herein, the pressure boundary is formed by manufacture of the housing ofconventional fluid pressure containment materials. The housing 20, suchas one manufactured from steel, has an inlet interface 30, shown as aninlet flange to the upstream fluid piping and a discharge interface 32,shown as a discharge flange to the downstream fluid stream piping. Theflow directing insert 14, possibly formed from unlisted materials, arewholly within the housing 20. The insert 14 is sealed to the housing 20at an inlet seal 34 at the inlet 24 and at a discharge seal 36 at thedischarge 26, maintaining separation between the fluid flow F and thefluid pad B. The fluid flow F then enters the housing at the inletinterface flange 30 and flows through the flow directing insert 14,sealed from the fluid pad B at the inlet seal 34. Fluid flow exits theflow directing insert 14, sealed from the fluid pad at insert dischargeseal 36. Finally, the fluid flow exits the housing 20, sealed from theenvironment at the discharge interface flange 32.

Brittle materials are typically unsuitable for pressure operations asthey cannot withstand the tensile stresses resulting from pressuredifferentials imposed thereon. By maintaining pressure both within andwithout the insert, and a pressures not too dissimilar to one another,stresses are minimized or eliminated.

Accordingly, the flow directing insert 14, such as that manufactured ofbrittle material, is immersed in the fluid pad B at pad pressureboundary pressures P2 near those at the process flow conditions P1,limiting the pressure differential (P1−P2) across the insert 14.

In one embodiment, and with reference to FIG. 1B, the pad pressure P2can be balanced to the fluid flow pressure P1 by placing a bleed port 38in the insert 14 on an erosion-protected area, such as on the insidebend 40, the bleed port having a restricted flow therethrough. Fluidfrom the fluid flow F will bleed through the bleed port 38 into thefluid pad B, balancing the pressure (P1=P2) across the insert,eliminating differential pressure stresses and minimizing stressoverall.

With reference to FIG. 2A, so as to enable detection of a failure alongthe insert, the pad pressure can be set to a threshold pressure P2, anychange therein, particular that approaching process pressure P1signaling a failure.

Further, and with reference to FIG. 2B, in another embodiment, so as toenable detection of failure along the insert, the pad pressure P2 can beset to a threshold pressure that is different from that of the processpressure P1; a differential pressure dP (dp< >0) of about 100 psi (700kPa) is deemed sufficient to detect a breach. Upon failure anywheretherealong, the pad P2 pressure will equilibrate with the gas processpressure P1 and P1−P2 with be about zero (|dp|=0). A pressure monitor orpressure monitoring devices, such as a pressure transducer ortransducers, can have a set point for differential pressure betweenprocess and pad pressures or for a change in pad pressure.

Alternatively, the pad pressure P2 can be controlled using a regulator50 using the process pressure P1 as a reference pressure, the regulatorincreasing the fluid pressure P2 in the pressure chamber as the processpressure P1 increases. The process pressure P1 can be tapped into thefluid flow F. As shown, P1 is monitored at about the inlet interface 30.A differential pressure can be maintained, such as a lower pad pressureP2 to a higher process pressure P1. Failure of the insert would causethe pad pressure P2 to rise, signalling failure. A pressurized source 52of pad fluid B, or pressure connected to the pad fluid, is provided toregulate a make-up pressure P3 to the pad pressure. In anotherembodiment, the pad fluid is an incompressible fluid such as a liquid.

As shown in FIG. 3A, so as isolate the source fluid of the make-uppressure from the pad fluid, the system can further include anintermediate isolation chamber 54. The pad fluid can be a liquid whichis to be separated from a gaseous pressure maintenance fluid or gas. Thechamber 54 and make-up source act as a form of liquid accumulator. Thechamber 54 forms a cylinder that can be incorporated into the housing20. Regulated make-up pressure P3 can drive a piston 56, movable withinthe chamber 54, to displace pad fluid to and from fluid pad B andnecessarily vary the fluid pad pressure P2 as process pressure P1 variesinside the flow directing insert 14. The pressurized source of make-uppressure P3 can be supplied by a pressure tank or bottle havingpressurized fluid within such as gaseous nitrogen (N2).

As shown in FIG. 3B, the isolation chamber 54 can alternatively belocated external to the housing 20.

Turning to the FIG. 4, one can eliminate need for a regulator using apressure-differential reduction piston loop 60 comprising a steppedpiston 62 and wherein the intermediate chamber is corresponding steppedcylinder 64. Process pressure P1 of the fluid flow F, through processconnection 56 to the fluid flow F, is in fluid communication with andacts on a first smaller area A1 of stepped piston 62 in stepped cylinder64 to produce force F. Force F acts on a larger second area A2 of thestepped piston 62, which is in fluid communication with, and producing afluid pressure P2 on the fluid pad side, fluidly connected through padconnection 58 to the pressure chamber 22. Accordingly, the fluidpressure P2 is automatically maintained at a pressure lower than theprocess pressure P1. As the process pressure P1 varies, so does thefluid pad pressure P2, only at a lower, and differential, pressure dP.

With reference to FIG. 5, the insert 14 is removably installable intothe housing 20 and replaceable. The insert 14 is sealed to the housing20 using end ring seals 70, 70 between each of the insert's inlet anddischarge ends 24,26, and an inside of the housing. The seals 70,70 sealthe insert 14 to the housing and separate the fluid flow F from thefluid pad B.

In an embodiment, the housing's pressure chamber 22 houses the insert 14and forms a first annular base to which the inlet end 24 of the insertis fit, a ring seal 70 being located therebetween. The first annularbase is aligned with, and formed about, the inlet interface 34. A secondannular base is provided at the discharge interface for sealing with theother discharge end 26 of the insert 14. A second ring seal 70 locatedtherebetween. In this embodiment the inlet and discharge ends 24,26 ofthe insert 14 are formed with flanges 71 for corresponding placement andsandwiching of the ring seal 70 between the insert 14 and the housing20.

As shown in the exploded view of FIG. 5, for installation of an insert14 into the housing 20, the housing can be formed in four components, amain body 72, an inlet body 74, a discharge body 76, and an accessclosure 78.

The insert 14 can be initially fit to the discharge body 76 andinstalled through an outlet port 90 of the main body 20. The dischargebody 76 is sealed thereto using conventional flange ring seal 80. Theflanged discharge end of the insert 14 is secured to the discharge body76 using an insert seal 70 and a retainer ring 81. That portion of thedischarge body 76 within the pressure chamber 22 forms the dischargeinterface 36. The retainer ring 81 clamps the insert's flange 71 to thedischarge interface 36 of the discharge body 76. With reference to FIGS.5A, 5B and 5C, the retainer ring 81 can be configured in one of avariety of two or more sectional pieces 82, as known in the art, so asto be arranged about the insert, yet form a substantially continuousclamp about the flange 71. FIG. 5A illustrates two sectional pieceswhile FIG. 5C shows four sectional pieces. The sectional pieces overlapand fasteners secure them together and to the underlying structure.

The inlet body 14 can be fit to an inlet port 79 of the main body 20 andsealed thereto using conventional flange ring seal 80 for forming asealed housing 20. That portion of the inlet body within the pressurechamber 22 forms the inlet interface 34. The inlet end 24 of the insert14 can be guided through an outlet port 90, aligning the inlet end ofthe insert with the inlet interface 34.

As shown in better detail in FIG. 6, an insert ring seal 70 is arrangedbetween the inlet end 24 of the insert 14 and the inlet interface 34. Aretainer ring 81 can be guided through an access port 90 for clampingthe insert's flange 71 to the inlet interface 34.

Once the inlet end 24 of the insert 14 is secured, the access closure 78can be secured to the main body 72 to seal the access port 92 and formthe pressure chamber 22.

The housing 20 is now closed to seal and form the fluid pad B. Thehousing closure is sealed and re-closable for permitting installationand replacement of the flow directing insert 14.

The arrangement for the inlet and outlet is arbitrary and can bereversed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. Flow directing apparatusfor conveying a fluid flow comprising: a housing forming a pressureboundary; and a flow directing insert fit sealably within the housingfor forming a pressure chamber about the insert and between the insertand the housing, the insert having an inlet end for receiving the fluidflow and a discharge end for discharging the fluid flow.
 2. The flowdirecting apparatus of claim 1 wherein the insert is replaceable.
 3. Theflow directing apparatus of claim 1 wherein: the inlet end is sealed tothe housing at an inlet seal; and the discharge end is sealed to thehousing at a discharge seal.
 4. The flow directing apparatus of claim 1wherein: the fluid flow contains particulates; and the insert is a wearresistant material resistive to erosion from the particulates.
 5. Theflow directing apparatus of claim 4 wherein the wear resistant materialis a non-ductile material.
 6. The flow directing apparatus of claim 5wherein the wear resistant material is a ceramic.
 7. The flow directingapparatus of claim 1 wherein the fluid flow has a process pressure andthe pressure chamber has a pad pressure.
 8. The flow directing apparatusof claim 7 further comprising a pressure monitor connected to thepressure chamber for detecting a pressure change in the pad pressurebeing indicative of failure of the insert.
 9. The flow directingapparatus of claim 7 wherein a pressure differential is maintainedbetween the process pressure and the pad pressure.
 10. The flowdirecting apparatus of claim 9 further comprising: a make-up pressuresource in fluid communication with the pressure chamber for maintainingthe pressure differential between the process pressure and pad pressure.11. The flow directing apparatus of claim 1 wherein the fluid flow has aprocess pressure and the pressure chamber is maintained at a padpressure, further comprising: a pad pressure maintenance system formaintaining the pad pressure relative to the process pressure.
 12. Theflow directing apparatus of claim 11 further comprising a pressuremonitor connected to the pressure chamber for detecting a pressurechange indicative of failure of the insert.
 13. The flow directingapparatus of claim 11 wherein the pad pressure maintenance systemfurther comprises a bleed port formed in the insert for pressuremaintenance, with restricted flow therethrough, between the fluid flowand the pressure chamber.
 14. The flow directing apparatus of claim 11wherein the pad pressure maintenance system further comprises a make-uppressure source and a regulator for introducing make-up pressure asnecessary to maintain a differential pressure between the fluid flow andthe pressure chamber.
 15. The flow directing apparatus of claim 11wherein the pad pressure maintenance system further comprises: a make-uppressure source and a regulator for introducing make-up pressure asnecessary to maintain a differential pressure between the fluid flow andthe pressure chamber.
 16. The flow directing apparatus of claim 11wherein the pressure chamber contains a fluid pad of liquid and the padpressure maintenance system further comprises: a make-up pressure sourceof gas at a make-up pressure; and a isolation chamber forming a cylinderand having a piston movable therein, the piston intermediate the make-uppressure source and the fluid pad.
 17. The flow directing apparatus ofclaim 16 wherein: the chamber is stepped and the piston is stepped; andthe piston has a first smaller area in fluid communication with theprocess pressure and a larger second area in fluid communication withthe fluid pad. for automatically maintaining the pad pressure at apressure lower than the process pressure.
 18. The flow directingapparatus of claim 1 wherein the pressure chamber contains a fluid padof liquid.
 19. A flow bend in wellhead piping comprising the flowdirecting apparatus of claim
 1. 20. A flow bend in wellhead pipingcomprising the flow directing apparatus of claim 11.